1. Field of the Invention
The present invention relates to a liquid crystal display module, and more particularly, to a backlight unit of a liquid crystal display module and a method of selecting a viewing angle.
2. Description of the Related Art
In general, a liquid crystal display (LCD) device includes a liquid crystal display module, a driving circuitry for driving the liquid crystal display module, and a case. The liquid crystal display module consists of a liquid crystal display panel having liquid crystal cells arranged in a matrix configuration between two glass substrates, and a backlight unit for irradiating light onto the liquid crystal display panel. The liquid crystal display module includes optical sheets for transmitting light emitted from the backlight unit toward the liquid crystal display panel. Accordingly, the backlight unit and the optical sheets must be engaged with each other in an integral shape to prevent light loss and to protect the backlight unit from damage caused by external impact. Thus, the case for the LCD device encloses the back light unit and the optical sheets including an edge of the liquid crystal display panel.
FIG. 1 is a schematic perspective view of a liquid crystal display module according to the related art. In FIG. 1, a liquid crystal display module includes a support main 24, a backlight unit and a liquid crystal display panel 6 disposed along an inside of the support main 24, and a case top 2 for enclosing edges of the liquid crystal display panel 6 and a side surface of the support main 24.
The liquid crystal display panel 6 is comprised of an upper substrate and a lower substrate (not shown) with a liquid crystal injected between the upper substrate and the lower substrate. In addition, the liquid crystal display panel 6 is provided with spacers (not shown) for maintaining a uniform gap between the upper substrate and the lower substrate. The upper substrate of the liquid crystal display panel 6 is provided with a color filter, a common electrode, and a black matrix. The lower substrate of the liquid crystal display panel 6 is provided with signal wirings, such as data and gate lines (not shown), and a thin film transistor (TFT) is formed at an intersection between the data and gate lines. The TFT switches a data signal to be transmitted along the data line into the liquid crystal cell in response to a scanning pulse (i.e., a gate pulse) transmitted along the gate line. A pixel electrode is formed within a pixel area between the data and gate lines.
One side of the liquid crystal display panel 6 is provided with data and gate pad areas connected to the data and gate lines, respectively. A data carrier package 8 is mounted with a data driver integrated circuit 10 for applying a data signal to the data lines, and is attached onto the data pad areas. Similarly, a gate carrier package 4 is mounted with a gate driver integrated circuit (not shown) for applying a scanning pulse (i.e., a gate pulse) to the gate lines, and is attached onto the gate pad areas. In addition, an upper polarizing sheet (not shown) is attached onto the upper substrate of the liquid crystal display panel, and a lower polarizing sheet (not shown) is attached onto the lower substrate of the liquid crystal display panel 6.
The support main 24 is a molded product, and the inner side wall surfaces are molded to have stepped coverage faces upon which the backlight unit and the liquid crystal display panel are disposed. The backlight unit includes a lamp 20, a lamp housing 22 for enclosing the lamp 20, a light guide plate 16 for progressing a light inputted from the lamp 20 into the liquid crystal display panel 6, a reflective sheet 18 arranged at the rear side of the light guide plate 16, and optical sheets 14a, 14b, 14c, and 14d disposed on the light guide plate 16. Light generated from the lamp 20 is incident onto the light guide plate 16 via an incidence face formed at the side surface of the light guide plate 16. The lamp housing 22 is formed to enclose the lamp 20 and reflects light generated from the lamp 20 into the incidence face formed at the side surface of the light guide plate 16.
FIG. 2 is a cross sectional view along I–I′ of FIG. 1 showing a viewing angle distribution of a backlight unit according to the related art. In FIG. 2, the reflective sheet 18 functions to re-reflect light incident thereto through the rear side of the light guide plate 16 onto the light guide plate 16, thereby reducing light loss. Thus, if light from the lamp 20 is incident to the light guide plate 16, light having progressed into the lower surface and the side surface of the light guide plate 16 is reflected by the reflective sheet 18 to be transmitted toward the front side thereof.
When light incident to the liquid crystal display panel 6 is transmitted at a right angle, a large light efficiency can be obtained. Accordingly, a plurality of optical sheets 14a, 14b, 14c, and 14d (in FIG. 1) vertically raise light output from the light guide plate 16, thereby improving light efficiency. Thus, a lower diffusing sheet 14d is provided for diffusing light output from the light guide plate 16 onto an entire area, and an upper diffusing sheet 14a is provided for diffusing light transmitted through two prism sheets 14b and 14c to increase a progress angle of the light diffused by the lower diffusing sheet 14d vertically with respect to the liquid crystal display panel 6. Accordingly, light output from the light guide plate 16 is incident to the liquid crystal display panel 6 via the plurality of optical sheets 14a, 14b, 14c, and 14d. 
In FIG. 2, viewing angle distribution characteristics of light output from the backlight unit are dependent upon physical features of the backlight unit. For example, a shape of the lamp housing 22 determines an amount of light being incident onto the incidence face formed at the side surface of the light guide plate 16 and then output via the light guide plate 16. In addition, the light output by the light guide plate 16 is influenced by the plurality of optical sheets 14a, 14b, 14c, and 14d (in FIG. 1).
As shown in FIG. 1, the case top 2 is fabricated into a square band shape having a plane part and a side part that are bent perpendicularly to each other. Accordingly, the top case 2 is engaged with the edges of the liquid crystal display panel 6 and the support main 24.
During an assembly process of the liquid crystal display module, the reflective sheet 18 and the light guide plate 16 are sequentially disposed on the support main 24. Next, the optical sheets 14a, 14b, 14c, and 14d are disposed onto the securing part of the support main 24. Then, after the optical sheets 14a, 14b, 14c, and 14d are assembled onto the support main 24, the liquid crystal display panel 6 is safely loaded onto the optical sheets 14a, 14b, 14c, and 14d. Subsequently, the case top 2 is assembled in such a manner to enclose the edges of the secured liquid crystal panel 6 and the side surface of the support main 24.
Accordingly, the viewing angle distribution characteristics of the liquid crystal display module are obtained from the viewing angle distribution characteristics of the backlight unit based upon use of a single lamp.